Many people have asked me a variety of questions and this question pops up a lot. Why can you only attack certain strongholds after you have taken one? Well, I'm not sure if you have noticed it or not, but there is white dotted lines connecting the strongholds together. Those lines are there for a reason. If you have taken a stronghold, you can only take the the adjoining strongholds via the white line. For example, look at the picture below:

My guild can only attack (BMW) Kashmir or Jerusalem. So we have a choice of starting a war with another guild or attacking an extremely strong stronghold. So when selecting your first stronghold, make sure you make a wise choice.